Motoharu Miyashita

Effectiveness of AlGaAs/GaAs superlattices in reducing dislocation density in GaAs on Si

Abstract The effectiveness in reducing the dislocation density in a GaAs layer on a Si substrate (GaAs-on-Si) is investigated by using AlGaAs/GaAs superlattices grown by metalorganic vapor phase epitaxy (MOVPE). The degree of dislocation density reduction is compared among several types of AlGaAs/GaAs superlattices with various layer thicknesses, various numbers of layers and various AlAs content of AlGaAs layer. The thicker each layer is, the larger the number of layers, or the larger the AlAs content, the larger is the degree of dislocation density reduction. As a result, the dislocation density is reduced to 1×10 6 cm −2 by using five periods of (20 nm Al 0.85 Ga 0.15 As)/(100 nm GaAs superlattice). The reduction of the dislocation density and the degree of this effect can be explained by the crystal hardening of AlGaAs and the bending of dislocations at the AlGaAs/GaAs superlattice.

Effect of Employing Positions of Thermal Cyclic Annealing and Strained-Layer Superlattice on Defect Reduction in GaAs-on-Si

This paper describes the dependence of the dislocation density reduction effect on the employing position of either thermal cyclic annealing (TCA) or InGaAs-GaAs strained-layer superlattice (SLS) in GaAs-on-Si grown by metalorganic chemical vapor deposition (MOCVD). The dislocation density is reduced to one twenty-fifth of that in as-grown sample by the TCA as the position of TCA becomes farther than about 1.5 µm from the Si surface. The dislocation density is additionally reduced to one third by the SLS as the position of SLS becomes farther than about 2.0 µm. As a result, the dislocation density is reduced to 1.5 × 106 cm-2 by the combined use of TCA and SLS. The dislocation density reduction effect of TCA is determined mainly by the degree of residual stress. That effect of SLS is determined mainly by the degree of additional stress generated by SLS.

Influence of oxygen on the threshold current of AlGaAs multiple quantum well lasers grown by metalorganic chemical vapor deposition

Abstract The influence of oxygen incorporation into the epitaxial layers on the threshold current density of AlGaAs multiple quantum well (MQW) lasers grown by metalorganic chemical vapor deposition (MOCVD) is studied quantitatively. It is shown that reduction of the oxygen concentration under 1X10 17 cm -3 in the cladding layers is necessary to obtain low threshold current density for the MQW lasers emitting at 780 nm. The effective carrier lifetime measurement in the active layer by time-resolved photoluminescence (PL) spectroscopy is a simple and effective method to monitor the oxygen contamination in the epitaxial layers.

Reduction of interface contamination in regrown GaAs on AlGaAs using a novel two-step HCl gas etching process

A two-step HCl gas etching process followed by regrowth using metalorganic chemical vapor deposition (MOCVD) has been developed. Two-step HCl gas etching involves a low-temperature HCl gas treatment (LTT) followed by high-temperature HCl gas etching. Upon using this process, no carbon accumulation was detected at the interface between the etched Al 0.48 Ga 0.52 As layer and the regrown GaAs layer. Oxygen accumulation at the regrowth interface was reduced to less than one fifth by applying LTT. The dislocation density in the regrown GaAs layer was shown to be comparable to that found in the usual GaAs homoepitaxial layer. The results of carrier lifetime measurements in GaAs/AlGaAs regrown double-hetero (DH) structures indicated the excellent quality of both the regrown GaAs layer and the regrowth interface. It was thus demonstrated that by using this newly developed two-step HCl gas etching process, the crystalline quality of a regrown GaAs layer on AlGaAs can be sufficiently improved to be used as an active layer of optical devices

Surface morphology improvement of GaAs-on-Si using a two-reactor MOCVD system and an AlAs/GaAs low temperature buffer layer: an approach to crack-free GaAs-on-Si

Abstract Non-uniform thermal stress distributions due to surface defects can be the origin of crack formation for GaAs layers deposited on Si substrate. A two-reactor MOCVD system specifically designed for GaAs-on-Si has been successfully applied to reduce surface defects of GaAs layers on Si. Three different low temperature buffer layers (LTB) of GaAs, A1As and A1As/GaAs were examined in order to study further improvement effect on the surface morphology. An A1As/GaAs LTB was found to be the most effective for reducing the surface defects. The surface defect number in a GaAs layer on a 3 inch Si wafer is reduced from 1433 (GaAs LTB) to 488 by introducing the A1As/GaAs as a LTB. This resulted in crack-free material for GaAs thickness exceeding 5μm. The use of thermal cycle annealing and the InGaAs/GaAs strained layer superlattices (SLS) is also investigated.

Study of initial buffer layer in GaAs-on-Si growth

Abstract An AlAs/GaAs low temperature buffer-layer (LTB) has been found to be effective for reducing the density of pit-defects in the GaAs layer grown on Si, which are the origin of micro-cracks. SEM observation has indicated that the Si surface is covered more smoothly and more uniformly by the AlAs/GaAs LTB rather than by conventional GaAs LTB. Consequently, the pit-defect density was remarkably reduced by employing the AlAs/GaAs LTB and the micro-crack free GaAs-on-Si with a GaAs thickness of 5 μm has been obtained.

Crack-free and low dislocation density GaAs-on-Si grown by 2-reactor MOCVD system

Abstract A 2-reactor MOCVD system is effective to reduce the surface defect which is the trigger for the crack formation, that enables one to obtain a 7 μm thick and crack-free GaAs layer on a 3 inch Si substrate. The etch pit density of the GaAs layer on Si substrate is reduced to 5 × 10 5 cm −2 by the combination of thermal cycle annealing and 2 sets of strained-layer superlattice buffer layers. The minority carrier lifetime measured by time resolved photoluminescence is also studied. It is found that PL lifetime mapping is useful as a non-destructive dislocation evaluation method.

High-power operation of AlGaInP red laser diode for display applications

Substantial limitation of output power in AlGaInP based red broad area (BA) laser diode (LD) originates from an electron thermal overflow from an active layer to a p-cladding layer and fatal failure due to catastrophic optical mirror degradation during the LD operation. New red BA-LD was designed and fabricated. The LD chip had triple emitters in one chip with each stripe width of 60 um, and was assembled on Φ9.0 mm -TO package. The LD emitted exceeding 5.5 W at heat sink temperature of 25 °C and 3.8W at 45 °C under pulsed operation with frequency of 120Hz and duty of 30%, although the current product, which has a 40 um single emitter chip assembled on Φ5.6mm –TO, does 2.0 W at 25 °C. The lasing wavelength at 25 °C and 2.5W output was 638.6 nm. The preliminary aging test under the condition with the operation current of 3.56A, CW, auto-current-control mode (ACC), and the heat sink temperature of 20 °C (almost equal to the output of 3.5 W) indicated that the MTTF due to COMD was longer than 6,600 hours under CW, 22,000 hours under the pulse with duty of 30%.

Short wavelength limitation in high power AlGaInP laser diodes

In wavelength region of red color, luminous efficacy rapidly increases as wavelength shortens. In that sense, red laser diode (LD) with shorter wavelength is required for display applications. Experimental results for short wavelength limitation in AlGaInP LDs are shown and discussed in this paper. Broad area LDs with 625, 630, and 638 nm are successfully fabricated. Operation current versus output power (P-I) characteristics and its temperature dependence of 625 nm LD are inferior to that of 630 and 638 nm ones. The main reason might be carrier leakage, and the results indicate that additional countermeasures to carrier leakage should be adopted to realize a 625 nm LD with the same temperature characteristics as 630 and 638 nm LDs. Conversion efficiencies from input electrical power to luminous flux output of the LDs are also studied. 625 nm LD has low efficiency, though brightness of 625 nm light is 1.7 times of 638nm one with the same output power. And 630 nm LD shows better conversion efficiency at high luminous flux region than 638 nm one, though the P-I characteristics of 630 nm is worse than that of 638 nm one. The tendency is inverted at low flux region, indicating that the lasing wavelength of red LD for laser display should be chosen carefully.

High-power red laser diode for recordable DVDs

A kink mechanism of a red (658nm) laser diode (LD) has been investigated in order to achieve a higher power operation of over 200mW. The experimental results indicate that a main origin of the kink generation is due to the deviation of the refractive index step caused by the local heat generation at the stripe region. To reduce the heat generation at the stripe region, an extension of a cavity length of the LD is applied. The LD with the cavity length of 1500μm realizes a kink-free 200mW operation even at 80°C. Also, this LD shows a reliable pulsed operation of 230mW at 75°C and 250mW at 70°C for over 1700 hours. This is the highest power operation among narrow stripe 658nm LDs.